14. LIPIDS & EFAs Flashcards
This module covers: • The structural characteristics of lipids. • The dietary sources, functions, bioavailability and metabolism of lipids, including essential fatty acids (EFAs). • Deficiency states and the therapeutic uses that apply to EFAs.
What is the body fat composition of a lean healthy man compared to that of a severely obese individual?
The body of a lean healthy man is composed of roughly 16% fat, while the lipid content in severe obesity can account for up to 70% (or 57 kg) of body weight, mostly in adipocytes.
Why were fats credited with heart disease in recent times? What did it lead to?
In the 1950s, Ancel Keys declared that eating a high saturated fat diet would increase serum cholesterol and consequently lead to heart disease.
The American Heart Association (AHA) then recommended a diet low in total fat, especially saturated fat and cholesterol, and high in carbohydrates from grains, substituting animal fats for seed oils. This also resulted in the introduction of statins - one of the pharmaceutical industry’s most profitable drugs.
Name THREE functions of white adipose
tissue (WAT)?
- The secretion of hormones, growth factors, enzymes and cytokines
- the protection of organs
- a form of energy storage
- insulation to protect against temperature extremes.
Name FIVE forms of lipids in the body.
- Individual fatty acids.
- Triglycerides.
- Phospholipids — in every cell membrane.
- Cholesterol and steroid-based compounds (e.g. oestrogen).
- Sphingolipids — found in nerve cell membranes, e.g. myelin.
- Glycolipids — involved in cell identity (like a cell ‘passport’).
- Cerebrosides — glycosphingolipids found in the brain.
- Fat-soluble vitamins — A, D, E, K.
What are the functions of lipids?
- Energy (ATP) production — each gram of fat supplies the body with about 9 calories.
- Storage of energy reserves — fats are a more efficient form of storage energy than carbohydrates or proteins, so the body stores any excess energy as fat.
- Cell membrane structure — phospholipids and cholesterol stabilise cell membranes, whilst allowing a degree of fluidity which is crucial to the function of every cell.
- Thermal insulation in subcutaneous tissue and protection around organs.
- Steroid hormones — progestogens, androgens, glucocorticoids, mineralocorticoids and oestrogens are derived from cholesterol.
- Formation of eicosanoids — signalling molecules involved in a range of processes such as blood coagulation and inflammation.
- Growth and development — the brain is rich in arachidonic acid (AA) and docosahexaenoic acid (DHA).
- Constituents of nervous tissue structure (sphingomyelin).
- Aid to cell-signalling processes.
- Required for the absorption of fat-soluble vitamins.
What is the chemical structure of fatty acids?
Fatty acids are hydrocarbon chains with an acid group at one end and a methyl group at the other.
What is the difference in number of carbons between short-chain, medium-chain, long-chain and very long chain fatty acids?
Short-chain fatty acids - up to 5 carbons.
Medium-chain fatty acids - between 6–12 Cs; can travel directly to the liver where they can be used to create energy or ketones.
Long-chain fatty acids - between 14–22 Cs.
Very long-chain fatty acids - > 22 Cs; are used to build cell membranes.
How are short-chain fatty acids (SCFAs) produced? What are the most common SCFAs?
SCFAs are produced when dietary fibre is fermented in the colon.
Acetate, propionate and butyrate are the most common SCFAs.
Which short-chain fatty acid is particularly important for colon health and why?
- Butyrate is particularly important for colon health because it is the primary energy source for colonocytes. It supports the intestinal tight junctions.
- Butyrate is thought to have an anti-inflammatory effect on the colon.
The omega-6 fatty acid, arachidonic acid, is referred to as 20:4 w6. What does it signify?
The omega system uses the number of carbon atoms, the number of double bonds, and the number of carbons from the omega end to the first carbon in the double bond.
What is hydrogenation and its impact on health?
Hydrogenation is the process by which hydrogen atoms are added to unsaturated fats and oils.
When oils are made into solid spreads, hydrogenation turns the natural fatty acid into unnatural forms (i.e. trans fats) which are damaging to health.
Describe the structure of saturated fatty acids.
Contain no C-C double bonds. All the carbons are completely saturated with hydrogen bonds. Solid at room temperature.
Unsaturated fatty acids structure
Contain one or more double bonds between carbons. Liquid at room temperature.
Monounsaturated fatty acids structure
Have one double bond in the chain.
Polyunsaturated fatty acids structure
Have several double bonds
Why is the number of double bonds in a fatty acid important?
The more double bonds there are in a fatty acid, the less stable it is, increasing susceptibility to oxidation.
How are unnatural trans fatty acids produced and in which types of foods are they typically found?
Unnatural trans fatty acids are produced by high temperatures and hydrogenation. They are found in margarine, processed foods and refined vegetable oils.
What are the effects of trans fats on the body?
- Trans fats stiffen cell membranes, making them prone to oxidation. This also alters their protective action and permeability, impeding normal cell function.
- Trans fats alter blood triglyceride and cholesterol profiles and are linked to an increased risk of cardiovascular disease, insulin resistance and cancer.
Are trans fats saturated or unsaturated?
Trans fats are unsaturated, but behave like saturated fats because of their unkinked shape.
What is the difference between the cis and trans fatty acids configuration?
– Cis configuration = the H atoms are on the same side of the double bond. The majority of natural fats are cis.
– Trans configuration = the H atoms are on opposite sides of the double bond.
Give an example of a natural trans fat, its benefits and where it can be found.
Conjugated linoleic acid (CLA) is a natural trans fat found in grass-fed meat and dairy products. Studies indicate CLA helps increase lean muscle mass and decrease body fat.
What is the major form of dietary fat, and the form in which fat is stored in the body?
Triglycerides (TGs). They circulate in the blood when released for energy.
Triglycerides (TGs) structure
TGs are lipid molecules made up of one unit of glycerol and three fatty acids. The three fatty acids can differ in length (number of carbon atoms) and degree of saturation (number of hydrogen molecules attached).
When does the body synthesise triglycerides and what has high levels of triglycerides in the blood been linked to?
The body synthesises triglycerides whenever caloric intake exceeds energy requirements.
High levels of triglycerides in the blood have been linked to atherosclerosis, and hence heart disease and stroke.
What is lipogenesis and where does it take place?
Lipogenesis is the process through which acetyl-CoA is converted to triglycerides for storage in fat. Three fatty acids are bound to glycerol and stored as triglycerides.
The sites of fatty acid synthesis are the liver, adipocytes, kidneys and lactating mammary glands.
What is lipolysis?
When dietary energy is limited, the fatty acids from triglycerides are mobilised from adipocytes into circulation.
Triglycerides are hydrolysed by lipase into fatty acids and glycerol for use in the body.
Name the hormones that
a) stimulates lipolysis
b) antagonises lipolysis
a) Stimulated by:
- Adrenaline, noradrenaline.
- Adrenocorticotropic hormone (ACTH).
- Glucagon and growth hormone.
- Thyroid-stimulating hormone (TSH) and thyroxine.
b) Antagonised by:
Insulin (antagonises the lipolytic effects of these hormones). As a result, insulin resistance (e.g. Type 2 diabetes) = central adiposity.
Describe the process how fatty acids can be broken down to produce energy
- Fatty acids cross the cell membrane (carnitine facilitates this), traverse the cytosol and reach the mitochondria.
- The fatty acids undergo beta-oxidation and are broken down into 2-carbon blocks as acetyl-CoA, which is oxidised via the Krebs cycle to CO2 and H2O.
- Energy is then generated using the electron transport chain.
What happens when carbohydrate levels are low in the body?
When carbohydrate levels are low, fat becomes the primary fuel for energy production (fatty acids or ketone bodies).
Ketone synthesis becomes necessary because the brain cannot metabolise fatty acids.
Ketones are made when glucose is in short supply. This occurs overnight, and during dieting or fasting
What is ketogenesis? Name TWO ketones.
A process when acetyl-CoA is converted to the ketones acetoacetate or β-hydroxybutyrate (β-OHB).
Acetoacetate can undergo decarboxylation to another ketone acetone.
How much carbohydrates needs to be consumed for the body to enter ketosis?
For most adults, this happens when carbohydrates are restricted to less than around 40 g a day.
What are the health benefits of ketosis?
Ketosis is linked with health benefits including weight loss, and the management of epilepsy, Parkinson’s and Alzheimer’s disease.
What is the difference between nutritional ketosis and ketoacidosis?
Ketoacidosis - an unstable and dangerous condition that develops when your body doesn’t have enough insulin to allow blood sugar into your cells for use as energy.
Describe the process of triglyceride digestion until its storage in adipose tissue.
In the stomach and small intestine, triglycerides are separated into glycerol and fatty acids. The resulting two free fatty acids and monoglyceride are transported into enterocytes, where they are rebuilt in the cell, packaged into chylomicrons and transported via the lymphatic system to the bloodstream.
The fatty acids can be used or stored in adipose tissue.
What aids triglyceride digestion?
The digestion of triglycerides is aided by gastric lipase in the stomach and pancreatic lipase in the duodenum, which act to separate the glycerol and fatty acids.
This process is facilitated greatly by the emulsifying action of bile, which increases the surface area of fat droplets.
What can we do to optimise lipid digestion?
- Chew adequately and avoid drinking with meals.
- Increase bile production by optimising stomach acid levels via zinc and B6-rich foods, bitter foods (e.g. chicory, rocket); stress management.
- Choleretics (increase bile production) and cholagogues (increase bile flow); e.g. dandelion, artichoke and turmeric.
- Ensure good hydration to support bile flow.
- Increase glycine and taurine, which are components of bile. Good sources include legumes, sea vegetables, spinach and eggs.
- Olive oil can stimulate bile secretion.
What was the result of dietary guidelines recommendations for reducing the intake of total fat and dietary fat (>10% of energy)?
Low-fat diets led to fat in foods being replaced with refined carbohydrates and sugar.
Without adequate energy from fat, people struggle to be sufficiently satiated. This has resulted in the consumption of ultra-processed foods.
High carbohydrate diets led to the highest mortality rates.
What can we advise clients regarding fat intake in their diet?
Eating fats from natural, unrefined foods should be the priority. Fat in the diet should be a mixture of saturated, monounsaturated and polyunsaturated fats, but absent of trans fats.
Fat-soluble antioxidants, e.g. vitamin E (sunflower seeds, almonds and wheat germ), are important when including fats in the diet.
Focus on the quality of the fat and combine with foods naturally rich in antioxidants.
List THREE benefits of including good amounts of healthy fats in the diet.
- Greater satiety value.
- Sources of essential fatty acids.
- Sources of choline (needed to synthesise phosphatidylcholine).
- Sources of essential fat-soluble vitamins and phytonutrients.
- Greater flavour enhancement in cooked food.
Name FOUR dietary sources of healthy fats.
- Fruit — avocado, olives.
- Seeds — chia, flax, pumpkin, hemp, seed butters.
- Seed oils — flax oil, chia oil, hemp oil, sunflower oil, olive oil.
Ensure oils are cold pressed. - Nuts — almonds, cashews, walnuts, Brazil nuts, nut butters.
- Other — coconut oil, grass-fed meat.
- Oily fish — salmon, mackerel, anchovies, sardines, herring.
Tryglycerides, composition & application in practice:
What are the benefits of coconut oil?
Coconut oil contains medium-chain triglycerides (MCTs) that increase the number of calories burned compared to longer-chain fatty acids.
Coconut oil contains 50% lauric acid. Monolaurin is formed from lauric acid. Both substances have
- antibacterial, antiviral and antifungal properties.
- ↑ HDL cholesterol, ↓ LDL cholesterol.
- Positive outcomes in epilepsy and Alzheimer’s disease.
What is the best fat for high temperature cooking? Give examples.
Due to the lack of double bonds in saturated fatty acids, they are considered more stable and less prone to oxidation / rancidity.
Coconut oil, butter and ghee contain saturated fats that can tolerate being heated and are preferable for cooking.
Frying foods in fat promotes free radical formation - ideally avoid.
